Remove duplicate work item attachment migration from owner branch

src/db/migrations/013_work-item-attachments.ts

@@ -1,17 +0,0 @@
-import type { Database } from 'bun:sqlite';
-
-import { tableHasColumn } from './helpers.js';
-import type { SchemaMigrationDefinition } from './types.js';
-
-export const WORK_ITEM_ATTACHMENTS_MIGRATION: SchemaMigrationDefinition = {
-  version: 13,
-  name: 'work_item_attachments',
-  apply(database: Database) {
-    if (!tableHasColumn(database, 'work_items', 'attachment_payload')) {
-      database.exec(`
-        ALTER TABLE work_items
-        ADD COLUMN attachment_payload TEXT
-      `);
-    }
-  },
-};